1. Field of the Invention
The invention pertains to the field of semiconductor devices. More particularly, the invention pertains to a semiconductor laser with a low beam divergence.
2. Description of Related Art
High power semiconductor lasers play an important role in telecommunication systems, serving as pumps, fiber amplifiers and in other applications.
To obtain a low power density per facet and a low beam divergence for an edge-emitting laser, generally an extended waveguide is used. However, significant narrowing of the far field pattern is limited by multi-mode laser radiation.
Prior art in the field of edge-emitting lasers with a low beam divergence includes the concept of a leaky wave diode laser that, in principle, obtains low beam divergence. An example of this prior art is U.S. Pat. No. 4,328,469, issued May 4, 1982, entitled xe2x80x9cHIGH OUTPUT POWER INJECTION LASERSxe2x80x9d. This patent discloses a heterostructure injection laser with an active layer sandwiched between a pair of intermediate index layers. A layer with a very thin low refractive index and high bandgap may be located between an active layer and an intermediate layer. The thin layer may be applied in various combinations to produce fundamental mode guiding effects.
The major disadvantage of such devices is an extremely small confinement factor of the fundamental mode. One cannot fabricate a high power laser based on this effect. Therefore, there is a need in the art for a laser realizing both a low beam divergence and high power output.
A semiconductor laser having a low beam divergence is disclosed. The laser includes at least one waveguide comprising an active layer generating an optical gain by injection of a current, a photonic band gap crystal having the refractive index modulation in the direction perpendicular to the propagation of the emitted light, and at least one defect. The active layer is preferably placed within the defect. The photonic band gap crystal and the defect are optimized such that the fundamental mode of laser radiation is localized at the defect and decays away from the defect, while the other optical modes are extended over the photonic band gap crystal. Localization of the fundamental mode at the defect results in the relative enhancement of the amplitude of the mode with respect to the other modes. Therefore, there is a larger confinement factor of the fundamental mode as compared to the confinement factor of the other modes. This enables efficient single-mode lasing from the laser having an extended waveguide.